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Message-ID: <4e83480731b937cea479f688029560444b9cb66a.camel@linux.ibm.com>
Date: Wed, 23 Dec 2020 19:03:18 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
stephen.smalley.work@...il.com, casey@...aufler-ca.com,
agk@...hat.com, snitzer@...hat.com, gmazyland@...il.com,
paul@...l-moore.com
Cc: tyhicks@...ux.microsoft.com, sashal@...nel.org, jmorris@...ei.org,
nramas@...ux.microsoft.com, linux-integrity@...r.kernel.org,
selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v9 2/8] IMA: add support to measure buffer data hash
On Sat, 2020-12-12 at 10:02 -0800, Tushar Sugandhi wrote:
> The original IMA buffer data measurement sizes were small (e.g. boot
> command line), but the new buffer data measurement use cases have data
> sizes that are a lot larger. Just as IMA measures the file data hash,
> not the file data, IMA should similarly support the option for measuring
> the hash of the buffer data.
>
> Measuring in-memory buffer-data/buffer-data-hash is different than
> measuring file-data/file-data-hash. For the file, IMA stores the
> measurements in both measurement log and the file's extended attribute -
> which can later be used for appraisal as well. For buffer, the
> measurements are only stored in the IMA log, since the buffer has no
> extended attributes associated with it.
By definition, buffer data is only measured. Nothing new is added by
the above paragraph. Please remove it.
>
> Introduce a boolean parameter measure_buf_hash to support measuring
> hash of a buffer, which would be much smaller, instead of the buffer
> itself.
Like the patch Subject line use "the buffer data hash" instead of the
"hash of a buffer".
There's no need to include the boolean parameter name
"measure_buf_hash". Please remove it.
>
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Reviewed-by: Tyler Hicks <tyhicks@...ux.microsoft.com>
> ---
> security/integrity/ima/ima.h | 3 +-
> security/integrity/ima/ima_appraise.c | 2 +-
> security/integrity/ima/ima_asymmetric_keys.c | 2 +-
> security/integrity/ima/ima_main.c | 38 +++++++++++++++++---
> security/integrity/ima/ima_queue_keys.c | 3 +-
> 5 files changed, 39 insertions(+), 9 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index e5622ce8cbb1..fa3044a7539f 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -268,7 +268,8 @@ void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
> struct ima_template_desc *template_desc);
> void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> const char *eventname, enum ima_hooks func,
> - int pcr, const char *func_data);
> + int pcr, const char *func_data,
> + bool measure_buf_hash);
Please abbreviate the boolean name to "hash". The test would then be
"if (hash == true)" or "if (hash)".
> void ima_audit_measurement(struct integrity_iint_cache *iint,
> const unsigned char *filename);
> int ima_alloc_init_template(struct ima_event_data *event_data,
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 8361941ee0a1..46ffa38bab12 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -352,7 +352,7 @@ int ima_check_blacklist(struct integrity_iint_cache *iint,
> if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
> process_buffer_measurement(NULL, digest, digestsize,
> "blacklisted-hash", NONE,
> - pcr, NULL);
> + pcr, NULL, false);
> }
>
> return rc;
> diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
> index 1c68c500c26f..a74095793936 100644
> --- a/security/integrity/ima/ima_asymmetric_keys.c
> +++ b/security/integrity/ima/ima_asymmetric_keys.c
> @@ -60,5 +60,5 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
> */
> process_buffer_measurement(NULL, payload, payload_len,
> keyring->description, KEY_CHECK, 0,
> - keyring->description);
> + keyring->description, false);
> }
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index e76ef4bfd0f4..0f8409d77602 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -779,7 +779,7 @@ int ima_post_load_data(char *buf, loff_t size,
> }
>
> /*
> - * process_buffer_measurement - Measure the buffer to ima log.
> + * process_buffer_measurement - Measure the buffer or the buffer data hash
> * @inode: inode associated with the object being measured (NULL for KEY_CHECK)
> * @buf: pointer to the buffer that needs to be added to the log.
> * @size: size of buffer(in bytes).
> @@ -787,12 +787,23 @@ int ima_post_load_data(char *buf, loff_t size,
> * @func: IMA hook
> * @pcr: pcr to extend the measurement
> * @func_data: private data specific to @func, can be NULL.
> + * @measure_buf_hash: measure buffer hash
^@...h: measure buffer data hash
> *
> - * Based on policy, the buffer is measured into the ima log.
> + * Measure the buffer into the IMA log, and extend the @pcr.
IMA always measures/appraises files and measures buffer data based on
policy. The above sentence succintly summarizes what
process_buffer_measurement() does. This patch adds support for
measuring the "buffer data hash". The following would be an
appropriate change.
* Based on policy, either the buffer data or buffer data hash is
measured
> + *
> + * Determine what buffers are allowed to be measured, based on the policy rules
> + * and the IMA hook passed using @func.
> + *
> + * Use @func_data, if provided, to match against the measurement policy rule
> + * data for @func.
> + *
> + * If @measure_buf_hash is set to true - measure hash of the buffer data,
> + * else measure the buffer data itself.
This patch should be limited to adding "buffer data hash" support.
These changes don't belong in this patch. Please remove.
> */
> void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> const char *eventname, enum ima_hooks func,
> - int pcr, const char *func_data)
> + int pcr, const char *func_data,
> + bool measure_buf_hash)
> {
> int ret = 0;
> const char *audit_cause = "ENOMEM";
> @@ -807,6 +818,8 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> struct ima_digest_data hdr;
> char digest[IMA_MAX_DIGEST_SIZE];
> } hash = {};
> + char buf_hash[IMA_MAX_DIGEST_SIZE];
> + int buf_hash_len = hash_digest_size[ima_hash_algo];
> int violation = 0;
> int action = 0;
> u32 secid;
> @@ -849,13 +862,27 @@ void process_buffer_measurement(struct inode *inode, const void *buf, int size,
> goto out;
> }
>
> + if (measure_buf_hash) {
^ if (hash) {
> + memcpy(buf_hash, hash.hdr.digest, buf_hash_len);
> +
> + ret = ima_calc_buffer_hash(buf_hash, buf_hash_len,
> + iint.ima_hash);
> + if (ret < 0) {
> + audit_cause = "measure_buf_hash_error";
I don't see a good no reason for defining a new audit cause. Use the
existing "hashing_error".
thanks,
Mimi
> + goto out;
> + }
> +
> + event_data.buf = buf_hash;
> + event_data.buf_len = buf_hash_len;
> + }
> +
> ret = ima_alloc_init_template(&event_data, &entry, template);
> if (ret < 0) {
> audit_cause = "alloc_entry";
> goto out;
> }
>
> - ret = ima_store_template(entry, violation, NULL, buf, pcr);
> + ret = ima_store_template(entry, violation, NULL, event_data.buf, pcr);
> if (ret < 0) {
> audit_cause = "store_entry";
> ima_free_template_entry(entry);
> @@ -890,7 +917,8 @@ void ima_kexec_cmdline(int kernel_fd, const void *buf, int size)
> return;
>
> process_buffer_measurement(file_inode(f.file), buf, size,
> - "kexec-cmdline", KEXEC_CMDLINE, 0, NULL);
> + "kexec-cmdline", KEXEC_CMDLINE, 0, NULL,
> + false);
> fdput(f);
> }
>
> diff --git a/security/integrity/ima/ima_queue_keys.c b/security/integrity/ima/ima_queue_keys.c
> index 69a8626a35c0..c2f2ad34f9b7 100644
> --- a/security/integrity/ima/ima_queue_keys.c
> +++ b/security/integrity/ima/ima_queue_keys.c
> @@ -162,7 +162,8 @@ void ima_process_queued_keys(void)
> entry->payload_len,
> entry->keyring_name,
> KEY_CHECK, 0,
> - entry->keyring_name);
> + entry->keyring_name,
> + false);
> list_del(&entry->list);
> ima_free_key_entry(entry);
> }
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